Once Tominaga Sei, the daughter of a doctor, she lived a normal life until her home was attacked because her father would treat anyone, regardless of who they supported in the growing conflict. Her beloved older brother was also killed in the attack, and Sei decided to fulfill her brother's dreams of joining the Shinsengumi where she would also avenge their deaths. Although she comes into the Miburoshi not skilled in sword fighting, Kondou and Hijikata admire her spirit (and Serizawa thinks that "he's" cute!) and she's permitted to join. She quickly grows close to Okita Souji, who discovers her secret but agrees to keep quiet after hearing her story.
A prodigy in sword fighting, Okita has a sweet, lighthearted side but when fighting his more serious side comes out. As captain of the First Squad, Sei comes under his guidance. He seems oblivious to Sei's feelings for him but is very protective of her, and in the beginning even tries to get her to leave the Miburoshi. He's closest to Hijikata and Saitou - for most of the series he and Saitou have been roommates, but at least Saitou seems to be a deep sleeper.
See our page here for more information on the Captain of the Third Squad, who is, after Sei and Souji, the next major character of the series.
Okita's closest friend is the vice-commander of the Shinsengumi, who he has known since childhood. Often seen as stern, Hijikata is the one who has to apply the force to accomplish what is needed and to instill discipline.
The bold and charismatic leader of the Shinsengumi, who shows wisdom and kindness but also has a firm strength. In flashbacks to Okita's childhood it shows that he thinks of Kondou as a father figure.
Yamanami Keisuke (Sannan)
The vice-commander is a quiet, kind man who romances Akesato. His death by seppuku shakes the Shinsengumi.
A leader in the Miburoshi, he's a loud, crude man who's often drinking and partying and pays Sei more attention than she's comfortable with, but it hides a calculating and shrewd mind. Later, he is assassinated, and his followers also killed or made to leave as the Miburoshi become the Shinsengumi.
Joining up later on in the series as a military advisor, he is a sly man who has an INTENSE crush on Hijikata, much to the vice-commander's chagrin, but like Serizawa it is a cover for his more secretive behavior.
Nagakura Shinpachi, Harada Sanosuke and Todou Heisuke - this trio is often seen together, causing mischief but all three are strong fighters who have been devoted to Kondou since their days at the Shieken dojo. They love to tease Sei, esp. Harada, who seems to have a crush on "him".
Inoue Genzabarou - A frequent companion to Nagakura, Harada and Todou, he is referred to as the oldest in the Shinsengumi but will always vigorously deny that he's old!